Electrical musical instrument



July 29, 1941. L. HAMMOND 2,251,051

ELECTRICAL MUSICAL INSTRUMEW" Filed July 15. 1939 VERY BRIGHT EEATOES ABE/6H 7' GENEEA MED/UM BRIGHT NEEATORS MELLOW DJUSTA EESON/HVT FILTER EXPRESS/ AND ArV/PL/F/EE TEEMULANT Patented July 29, 1941 UNITED STATES PATENT OFFICE ELECTRICAL MUSICAL INSTRUMENT Laurens Hammond, Chicago, Ill.

Application July 15, 1939, Serial 'No. 284,762

14 Claims.

My invention relates generally to electrical musical instruments and more particularly to an improved system for electrically generating tone signals of various qualities, and controlling their selective transmission and translation into sound.

It is an object of my invention to provide an improved electrical musical instrument in which there are a plurality of sets of generators of frequencies corresponding to the notes of the musical scale within the range of the instrument, each set generating tone signals of a different quality, each supplying these tone signals to a circuit individual to the generator, and in which the signal outputs of the sets may be mixed in any desired proportion.

A further object is to provide an improved electrical musical instrument in which depression of the key causes the generation of a plurality of tone signals by a plurality of sets of generators, and in which the relative amplitudes of the signals provided by the separate generators may be readily controlled.

A further object is to provide an improved electrical musical instrument in which a wide variety of desirable and interesting musical effects may be obtained.

Other objects will appear from the following description, reference being had to the accompanying drawing in which:

Figure 1 is a circuit diagram of representative portions of the complete 'musical instrument;

' Figure 2 is a fragmentary transverse sectional view of one of the generators.

The instrument of my invention may be described generally as comprising a plurality of sets of generators, each set being capable of generat-.

ing electrical signals corresponding to the fundamental frequencies of the notes of the musical scale within the range of the instrument. The sets of generators, however, are constructed so as to generate tone signals of different degrees of harmonic development. For example, one set of generators may generate tones which are very bright, a second set may generate tones of medium brightness, while the third set generates tones which are very mellow, approaching the tone quality of the flute, which has very little harmonic development.

Upon depression of a key, corresponding generators in each set are energized or rendered operative, but the outputs of the sets of generators are controllable so that if desired, only the signal from the generator in the very bright set is transmitted to the output circuit of the instrument and translated into sound. Or, only the signal from one of the other sets of generators is utilized to produce this sound, or the signals from two or more of the sets of generators may be combined in selected amplitude proportions so that the sound produced is composed of signals derived from a plurality of generators of different sets.

The combined output of the several sets of generators is fed to a common output circuit where means are provided for controlling the amplitude of the combined signal, and where adjustable resonant filter circuits may be utilized further to vary the over-all tone quality.

In Figure 1, the instrument is illustrated as including five sets of generators l0 to 14, although two or three sets may be sufficient for most purposes. Each set of generators includes a plurality of individual generators, in number corresponding to the number of notes in the gamut of the instrument, with the possible addition of anoctave or two of generators having fundamental frequencies corresponding to notes an octave or two higher than the highest octave for which keys are provided. These generators may be of any suitable type and construction, although for the purposes of the following description, the generators are assumed to be of the electrostatic type in which each generator consists of a rotating tone wheel with one or more pickup electrodes located adjacent the periphery of the tone wheel. The amplitude of the signal thus generated is determined by the direct current potential impressed upon the electrode. Such generators may be of the construction disclosed in my copending application, Serial No. 281,077, filed June 26, 1939, or as shown in the patents to Midgley, No. 2,112,291 or Bourn, Re. No. 19,702.

By having all of the tone wheels rotate at speeds in the order of seven revolutions per second, as disclosed in my aforesaid application, it is not essential that they be very accurately formed to the desired shape, and therefore it is commercially feasible to make an instrument in which there are two, three, five, or a greater number of sets of generators.

As generally illustrative of a type of generator which may be employed, Figure 2 shows a tone wheel l6 mounted on a shaft it which is rotated at a speed in the order of seven revolutions per second by suitable driving means. The tone wheel It has a plurality of projections 20 on its periphery, which rotates in close propinquity to pickup electrodes 22 which are insulated from a shielding housing 24 surrounding the tone wheel. The electrodes 22 are provided with terminals 28 external to the housing 24. The tone wheels l6 and their driving shafts l8 are insulated from the housing 24, and as a result, an alternating current signal is generated between the tone wheel and the housing 24, whenever a direct current potential is impressed upon one or more of the electrodes.

The shaft l8 preferably carries an eccentric magnetic disc 28 which rotates adjacent an electro-magnet 30. The magnet 30, when energized, attracts the disc 28 with greater force during approximately one half of its revolution than during the other half, thus alternately accelerating and retarding the shaft l8 during each revolution of the shaft. Such periodic acceleration and retardation of the tone wheel l6 attached to the shaft l8, results in slight periodic changes in the frequency of the generated signal which is recognized in the music produced as a vibrato effect, since its periodicity is in the order of seven cycles per second.

Each shaft, such as l8, may have secured thereto a number of tone wheels l6 determined by the gamut of the instrument, the tone wheels having the number of projections 20 required to produce tones of octave relationship, and there may be twelve shafts similar to l8 in each set of generators, one for each of the twelve semitones of an octave. Each of the sets of generators If] to l4 may supply its output signal to an individual amplifiersuch as the amplifiers 40 to 44, and the outputs of these amplifiers are supplied to a common conductor 46 forming a mixing channel, the amplitude of the signal derived from each amplifier 4U to 44 inclusive being determined by the setting of adjustable impedance controls 48, one of which is associated with the output of each of the amplifiers. The composite signal from the various amplifiers is supplied to suitable expression and tremulant control devices 59, and from thence through suitable adjustable resonant filter circuits 52 to a power amplifier 54, which in turn supplies a speaker 56.

The potentials impressed upon the terminals 26 are selectively determined by the operation of the keys of the instrument, three of which Al, A2 and A3, are illustrated in Fig. l as representative of the complete keyboard. These keys may be considered as controlling the notes of the pitch represented by their reference characters. Each key controls the operation of two switches by means of insulating actuator 59. Beneath each key is a flexible switch contact arm 60, a rigid contact arm 62 and a second flexible switch contact arm 64. The switch arm 60 normally makes contact with a bus bar 66 and is adapted, when the key is depressed, to make contact with the rigid switch arm 62. The lower switch arm 64 normally makes contacts with a bus bar 68, and breaks this contact when the key is depressed. The switch arm 64 may be held in depressed position by an insulating strip 10 attached to a shaft 12 which is adapted to be actuated by a sustaining pedal 14. The bus 66 is connected to a source of adjustable direct current potential Ba while thebus 6B is illustrated as being connected to a point of fixed direct current potential, illustrated as ground.

The switch arm 60 is connected by resistors RIO and RH with a conductor 16 which is connected to-anadjustable source of direct current potential 30. A condenser Cl is connected between ground and the junction of resistors RH] and RI I. A resistor R8 connects the rigid contact arm 62 with a conductor 18 while a resistor R9 connects the conductor 18 with the flexible switch contact arm 64.

The conductor 18 is connected to ground through a condenser C2 and a high resistance R2. The conductor I8 is connected to tenninals 25, one on each of the sets of generators ID to l4 inclusive, which are located adjacent the tone wheels generating signals having fundamental frequencies corresponding to the note Al. By means of a manually controlled switch 80, a conductor 82 may be connected to the conductor 18, the conductor 82 being connected to terminals 26, one on each of the sets of generators ill to l4 and adjacent the tone wheels which generate signals corresponding in fundamental frequency to the note A2, 1. e., a note one octave higher than the note Al. A similar coupler switch 84 is adapted to connect a conductor 86 to the conductor 18, the conductor 86 being connected to terminals 26, one on each of the sets of generators If] to M, and located adjacent the peripheries of the tone wheels generating signals having a fundamental frequency three times that of the note Al. Thus, the closure of the switch results in coupling the octave, while closure of the switch 84 results in coupling the third harmonic.

The key A2 controls switches which are identical to those operated by the key Al, and similar reference characters have therefore been applied to parts corresponding to tnose previously described. The circuits associated with the switch A2 are likewise similar to those for the key Al, except that the constants may, if desired, be of slightly different values.

The circuits for the key A2 control the potential upon the conductor 88 which corresponds to the conductor 78 for the key Al. Coupler switches 90 and 94 control the connection of conductors 92 and 96 to the conductor 88 in the same manner that the coupler switches 80 and 84 control the connection of the conductors 82 and 86 to the conductor 78. The connection of the conductors 92 and 96 to the terminals 26 of the various generators is similar to the connection of the conductors 82 and 86 to such terminals, except that the conductors 92 and 96 are connected to terminals 26 associated with tone wheels one octave higher.

Switches 80 and 90 as well as the corresponding coupler switches for all of the other key circuits are preferably operated by a common control, and similarly, the coupler switches 84 and 94 and similar switches associated with the other key circuits are operated by a common manually actuated element. In order not to introduce unnecessary complexity in the circuit diagram, the coupler switches and coupler circuits for the key A3 have not been shown.

The electromagnets 30, of which there is one for each of the twelve shafts incorporated in each set of generators, are connected in parallel and supplied with current from a source of adjustable potential Bd. This source thus provides a means common to all of the generators for controlling the degree of vibrato. The degree of vibrato on each set of generators may be individually controlled by a rheostat 98 associated with each set of generators, the rheostat being constructed so as to permit the electromagnets to be completely de-energized when desired.

In operation, the sets of generators are driven continuously either by individual synchronous motors or by a common constant speed motor through suitable gearing, and the various controls 48 adjusted to the positions necessary to produce the desired quality of music. When a very bright string quality tone is desired, the control #8 for the set of generators It may be set at its maximumgwhile the controls 58 for the other sets of generators are set for zero transmission of signal. Conversely, when a very mellow flute-like tone is desired the control 48 for the set of generators it will be set for maximum signal, while the remaining controls 48 will be set for minimum or zero signal.

By proper selective setting of the various controls 48, the desired signal mixture from the various generators may be obtained. Since the mixtures are of signals derived from different sources, the composite signal will produce a chorus effect desirable for the rendition of certain musical selections. Furthermore, the signals from each of the sets of generators will have slight vibrato shifts in frequency even when the vibrato electromagnets 30 are not energized, and the mixture of the signals from several generators will therefore be of a very complex and musically interesting nature.

By closure of the coupler switches, additional generators are rendered effective so that the quality of the sound produced is rendered additionally complex providing the musical effect of a large number of instruments playing simultaneously. While the controls 48 and the coupler switches 80 and 90 thus provide means for producing a wide variety of musical effects, the provision of the adjustable resonant filter circuits makes possible additional variation in tone color whenever desired, since these circuits will serve to reinforce certain frequencies, while attenuating other frequencies.

Any suitable tremulant device (such, for example, as disclosed in applicant's prior Patent No. 1,956,350) and an expression control device, preferably operated by a swell pedal, may be incorporated in the instrument, although for ordinary purposes, the tremulant device will be unnecessary since the vibrato effect is generally superior'to the tremulant effect and may take its place in the rendition of most types of music.

The key circuits employed are generally similar to those disclosed and claimed in my prior Patent No. 2,126,464, dated August 9, 1938, and operate in a similar manner to control the intensity envelopes of the notes. It will be understood that the condenser Cl is normally charged through the resistance RIO (which is of lower value than the resistance RH), to an extent determined by the setting of the adjustable direct current potential source Ba, so that upon depression of the key, the charge on the condenser Cl is changed by current flow through the resistance RIO, switch contact arms 60 and 62, resistance R8 and conductor 18.

The rate at which' the potential on the conductor l8 initially builds up to the potential of the condenser CI is determined by the relative values of the resistances RIO and R8 compared with the capacity of the condenser C2, and these elements, together with potentials of the direct current sources, determine the character of the attack of the note upon key depression. After the key has been depressed for a very short interval, the charges on the condensers Cl and C2 will become substantially equalized and therei rect current source Bo which, it will be noted, is applied to the conductor 18 through the resistors RH and Bill, the switch contact arms 60 and 6 2 and resistance R8. The potential of the source Bc will thus determine the amplitude of the signal during its steady state.

If the potential Be i made high relative to the potential of Be, the attack will be gradual, simulating that of wind instruments such as the pipe organ, whereas, if the potential of Ba is made high relative to the potential of Be, the amplitude of the signal will rise rapidly and then decay to a lower value, simulating the tone of percussive instruments such as the various plucked or struck string instruments. When the key is released, the potential of the conductor 78 drops rapidly to ground potential by flow of current through the resistor R9, the switch contact arm 64 and bus bar 58.

When it is desired to sustain the tones after release of the keys, the sustaining pedal I4 is depressed, thus rotating the shaft 12 clockwise and, through the insulating bar 10, holding the switch contact arms 64 depressed. As a result, the potentials upon the conductors 18 will be maintained except for the slow leakage through the high resistances R2 by which the conductors 18 are connected to ground. Thus, when the sustaining pedal is depressed, the notes will decay very slowly. The rate of decay will be logarithmic in character, since the condenser C2 tends to maintain the potential on the conductor 18, and the curve representing the drop in potential of the conductor "I8 is the characteristic logarithmic curve resulting from the discharge of a condenser through a resistance.

It will be apparent that by proper adjustment of the potential sources Ba and Be, and by making the various resistors and condensers of appropriate values, a wide variety of intensity envelopes may be readily obtained, thus greatly enhancing the variety of musical eifects obtainable by the use of the instrument. If desired, separate adjustable potential sources such as Ba and He may be provided for the different registers of the instrument. In this way, for example, the notes of the treble register may be made to have slow attack simulating a singing quality, whereas, the notes of the bass register may be made to have percussive attack, whereby very interesting and unusual efiects may be obtained.

While I have illustrated but a single form of generator, it will be understood that the generators may be of any suitable construction in which the potential upon one terminal of the generator determines the amplitude of the signal produced thereby. Similarly, variations may be made in the other portions of the instrument disclosed without departing from the fundamental principles of the invention. I therefore desire by the following claims, to include within the scope of my invention all such similar and equivalent constructions whereby substantiaily the results of my invention may be obtained by the use of substantially the same or equivalent means.

I claim:

1. For use in an electrical musical instrument having electroacoustic translating means, a plurality of sets of complex wave electrical generators, each set including generators of frequency range substantially the same as the gamut of the complete instrument, the tone qualities of the signals produced by the generators of the diii'erent sets diflerlng from one another, key controlled circuits for selectively energizing corresponding generators in each of said sets of generators, an output circuit for each of said sets of generators, an output circuit common to all of said sets of generators for supplying a signal to the electroacoustic translating means, and means for selectively controlling the degree of coupling between the output circuits of said sets of generators and said common output circuit.

2. For use in an electrical musical instrument having electroacoustic translating means, a plurality of sets of complex wave electrical generators, each set including generators of frequency range corresponding substantially to the gamut of the complete instrument, the tone qualities of the signals produced by the generators of the difierent sets differing from one another, key controlled circuits for rendering corresponding generators in each of said sets of generators effective to supply a signal, an output circuit for each of said sets of generators, an output circuit common to all of said sets of generators for supplying a signal to the electroacoustic translating means, and means for selectively controlling the degree of coupling between the output circuits of said sets of generators and said common output circuit.

3. In an electrical musical instrument, the combination of a plurality of sets of complex wave electrical generators, the generators of each set producing musical signal impulses of similar complex wave form and differing from the wave form of the signals produced by generators of other sets, key controlled parallel circuits for energizing corresponding generators in each of said sets of generators, an amplifierlfor the output of each of said sets of generators, a transmission circuit common to the outputs of all of said amplifiers, and selectively adjustable volume control means coupling said amplifiers respectively to said transmission circuit.

4. In an electrical musical instrument, the combination of a plurality of sets of complex wave form electrical generators, the generators of each set producing complex musical signal impulses of similar wave form and differing from the Wave form of the signals produced by generators of other sets, key controlled parallel circuits for causing generators of corresponding fundamental frequency in each of said sets of generators to supply a signal, a transmission circuit common to the outputs of all of said sets of generators, and selectively adjustable Volume control means coupling said amplifiers respectively to said transmission circuit.

5. The combination set forth in claim 4 in which each set of generators is provided with means for introducing a vibrato effect, a control common to all of said sets of generators to vary the effectiveness of said means, and controls individual to each of said sets of generators to vary the effectiveness of said means.

6. In an electrical musical instrument having a plurality of sources of tone frequency impulses, means connected with each of said sources for varying the frequencies generated by said source at a vibrato periodicity, a control common to all of said sets of generators for adjusting the effectiveness of said means, and a control individual to each of said generators for varying the effectiveness of said means.

'7. In an electrical musical instrument having at a vibrato periodicity, and a control common to all of said sets of generators for adjusting the effectiveness of said means.

8. In an electrical musical instrument, the combination of a set of electrical generators each being capable of generating musical signals of high harmonic development, a second set of generators each capable of generating a signal of relatively slight harmonic development, key controlled means for simultaneously rendering effective generators of the same fundamental frequency in each of said sets, and adjustable means for mixing the signals from said sets of generators in any desired relative proportions.

9. In an electrical musical instrument, the combination of a set of electrical generators each being capable of generating musical signals of high harmonic development, a second set of gen erators each capable of generating a signal of relatively slight harmonic development, key controlled means for simultaneously rendering effective generators of corresponding pitch in each of said sets, coupler circuits for increasing the number of generators rendered effective by said key controlled means, and adjustable means for mixing the signals from said sets of generators in any desired relative amplitude proportions.

10. In an electrical musical instrument, the combination of a plurality ofsets of electrical generators, the generators of a set generating musical signals of tone quality differing from that of the signals generated by each of the other sets of generators, key controlled circuits for selectively energizing generators of corresponding pitch of each of said sets of generators, an output circuit common to all of said generators, and means for individually adjusting the relative amplitudes of the signals derived from said sets of generators.

11. In an electrical musical instrument, the combination of a plurality of sets of electrical generators, the generators of a set generating musical signals of distinctive tone quality, key controlled circuits for selectively energizing groups of generators one from each of said sets of generators, an output circuit common to all of said'generators, means for individually adjusting therelative amplitudes of the signals derived from said sets of generators, and means in said common output circuit for varying the tone quality of the composite signal derived from said selectively energized groups of generators.

12. In an electrical musical instrument, the combination of a plurality of sets of electrical generators capable of generating complex tone signals of the fundamental frequencies of the notes of the musical scale, each set generating signals differing in tone quality from those generated by the other sets, key controlled circuits for rendering effective generators in each set of generators, a common output circuit, and mixing means for combining the output signals of said sets of generators and transmitting said signals to said common output circuit in selectively controllable relative amplitudes.

13. In an electrical musical instrument, the combination of a plurality of sets of electrical complex wave generators, key controlled circuits, each rendering simultaneously effective at least one of the generators in each set of generators, a common output circuit, and mixing means to combine the outputs of said sets of generators, and to transmit the combined outputs to said common output circuit in selectively controllable relative proportions,

14. In an electrical musical instrument, the

' combination of a plurality of sets of electrical complex wave generators capable of generating tone signals of the frequencies of the musical scale, each of said sets generating tone signals of a degree of harmonic development diflering from that of the signals generated by other sets, key controlled circuits for simultaneously ren- 

